Method and system for coolant temperature control in a vehicle propulsion system

ABSTRACT

A vehicle propulsion system includes a prime mover having a coolant inlet and a coolant outlet, a coolant control valve having a valve inlet in communication with the prime mover coolant outlet, a first valve outlet, and a second valve outlet, a bypass flow path in communication with first valve outlet and the prime mover coolant inlet, a heat exchange flow path in communication with the second valve outlet and the prime mover inlet, a heat exchanger in the heat exchange flow path, a first temperature sensor in the bypass flow path for generating a first temperature signal, a second temperature sensor in the heat exchange flow path for generating a second temperature signal, and a controller for providing a coolant control valve command signal to the coolant control valve, using a normalized gain coefficient.

FIELD

The present disclosure relates to a method and system for coolant temperature control in a vehicle propulsion system.

INTRODUCTION

This introduction generally presents the context of the disclosure. Work of the presently named inventors, to the extent it is described in this introduction, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against this disclosure.

Vehicle propulsion systems may include thermal management systems which regulate the temperature of the prime mover such as an internal combustion engine and the like. Temperature management of an internal combustion engine may be important to optimize fuel economy, efficiency, reliability, and durability of, not only the engine, but also of the overall system.

Many thermal management systems for vehicle propulsion systems rely upon a flow of coolant passing through the engine that is regulated by a very simple thermostat. The ability of such a system to accurately and reliably maintain a desired, or target temperature for the engine is very crude. Response to temperature changes can be very slow and only control the temperature within a very wide range.

SUMMARY

In an exemplary aspect, a vehicle propulsion system includes a prime mover having a coolant inlet and a coolant outlet, a coolant control valve having a valve inlet in communication with the prime mover coolant outlet, a first valve outlet, and a second valve outlet, a bypass flow path in communication with first valve outlet and the prime mover coolant inlet, a heat exchange flow path in communication with the second valve outlet and the prime mover inlet, a heat exchanger in the heat exchange flow path, a first temperature sensor in the bypass flow path for generating a first temperature signal, a second temperature sensor in the heat exchange flow path for generating a second temperature signal, and a controller in communication with the first temperature sensor for receiving the first temperature signal, the second temperature sensor for receiving the second temperature signal, and the coolant control valve for providing a coolant control valve command signal to the coolant control valve. The controller is a closed loop controller with a gain coefficient, and the controller normalizes the gain coefficient.

In another exemplary aspect, the closed loop controller is a proportional/integral closed loop controller.

In another exemplary aspect, the gain coefficient is one of a proportional gain coefficient and an integral gain coefficient for the proportional/integral closed loop controller.

In another exemplary aspect, the controller normalizes the gain coefficient based upon a ratio of a predetermined difference in values between a first temperature signal and the second temperature signal and a current difference in values between a first temperature signal and the second temperature signal.

In another exemplary aspect, the predetermined difference in values between a first temperature signal and the second temperature signal correspond to a first temperature signal value and a second temperature signal value which both correspond to the gain coefficient.

In another exemplary aspect, the second temperature sensor is downstream of the heat exchanger in the heat exchange flow path.

In another exemplary aspect, the bypass flow path and the heat exchange flow path combine to form a prime mover coolant inlet flow path at the prime mover coolant inlet.

In another exemplary aspect, the third temperature sensor is positioned in the prime mover coolant inlet flow path.

In this manner, thermal management of a prime mover in a vehicle propulsion system may be greatly improved and provide more reliable, responsive, and accurate control of temperature. The system temperature may then be continually optimized over a wide range of operating conditions. This enables more confidence which permits a prime mover to operate closer to a potential threshold temperature while reducing the risk of deviating from a target temperature. In turn, this enables improved fuel economy, efficiency, performance, reliability and durability of the components of the system. Further, this also significantly reduces the calibration workload that might be otherwise required.

Further areas of applicability of the present disclosure will become apparent from the detailed description provided below. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.

The above features and advantages, and other features and advantages, of the present invention are readily apparent from the detailed description, including the claims, and exemplary embodiments when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a thermal management system for a vehicle propulsion system;

FIG. 2A is a graph illustrating a temperature response to a condition change in a thermal management system;

FIG. 2B is a graph illustrating a temperature response to a condition change in a thermal management system in accordance with an exemplary embodiment of the present disclosure; and

FIG. 3 is a flowchart of a method in accordance with an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

Thermal management of a prime mover, such as, for example, an engine, motor, battery pack and/or the like, in a vehicle propulsion system may be critical for obtaining optimal performance, reliability and durability. FIG. 1 illustrates a thermal management system 100 in a vehicle propulsion system. The thermal management system includes a prime mover 102 that provides power for the vehicle propulsion system. The prime mover 102 may be, for example, an internal combustion engine, an electric motor, or the like without limitation. Operation of the prime mover 102 may require management of temperature in order to optimize efficiency, economy, performance and/or the like. The thermal management system 100 circulates a coolant throughout the system 100 as indicated generally by arrows 104 in a manner which enables management of the temperature of the engine. The coolant leaves the engine 102 at a coolant outlet 106 and flows to an inlet 108 of a coolant control valve 110. The coolant control valve 110 is in communication with a coolant control valve controller 112 which generates coolant control valve control signals 114 which determine the operation of the coolant control valve 110. The coolant control valve 110 is selectively operable to split the flow of coolant received at the coolant inlet 108 into a bypass path 116 and/or a heat exchange path 118. The bypass path 116 communicates between the coolant control valve 110 and an engine coolant inlet 120. The heat exchange path 118 includes a heat exchanger 122 that operates to transfer heat either from or to the coolant flowing through the heat exchanger 122. Since, in a preferred embodiment, the engine 102 may be an internal combustion engine which generates heat and which must have heat removed from the engine to optimize operation of the engine, the heat exchanger 122 may be a radiator that transfers heat from the coolant flowing through the heat exchanger 122 to the ambient atmosphere surrounding the heat exchanger 122.

The thermal management system 100 may operate in accordance with instructions generated by a control architecture. For example, the coolant control valve controller 112 may receive a first temperature signal, T1, from a first temperature sensor 124 that is positioned in the bypass flow path 116 and which senses the temperature of coolant flowing through the bypass flow path 116. The coolant control valve controller 112 may also receive a second temperature signal, T2, from a second temperature sensor 126 that is positioned in the heat exchange flow path 118 and which senses the temperature of coolant exiting the heat exchanger 122 in the heat exchange flow path 118. The coolant control valve controller 112 may further receive a third temperature signal, T3, from a third temperature sensor 128 that is positioned at the engine coolant inlet 120.

Based upon the first temperature signal, T1, the second temperature signal, T2, and the difference between the third temperature signal, T3, and a target engine coolant temperature the coolant control valve controller 112 may control the coolant control valve 110 in a manner that results in a split in the volume of flow between the bypass flow path 116 and the heat exchange flow path 118 which approaches a target temperature, T3, of the coolant entering the engine coolant inlet 120. In an exemplary embodiment, the coolant control valve controller 112 may operate as a proportional/integral closed loop controller The coolant control valve controller 112 may operate the coolant control valve 110 in accordance with the following:

dV=Kp×T _(error) +Ki×∫ _(t−1) ^(t) T _(error) dt   (1)

Where dV is the controller-determined change in the volume split between the bypass flow path 116 and the heat exchange flow path 118, Kp is a proportional coefficient, T_(error) is the difference in temperature between the target inlet temperature and the actual inlet temperature, and Ki is an integral coefficient. T_(error) may be determined according to:

T _(error) =T _(target) −T ₃   (2)

Where T_(target) is the desired or targeted coolant temperature at the engine coolant inlet 120 and T₃ is the actual coolant temperature at the engine coolant inlet 120.

In this manner, the thermal management system 100 may control the amount of heat removed from the prime mover 102 by diverting proportions of a stream of coolant exiting the prime mover 102 into two streams, the relative proportions of those streams may be adjusted with a closed loop controller that operates based upon an error or difference between a target coolant inlet temperature and an actual coolant inlet temperature. However, the effectiveness of this thermal management system 100 is based upon proportional and integral coefficients which are determined by calibrating those coefficients for a specific set of conditions. As those conditions change from that specific set of conditions, the coefficients which correspond to optimized prime mover performance at a new set of conditions also change. Any reduction in temperature control of the prime mover as a result of a change in operating conditions may have adverse effects on the fuel efficiency, economy, durability, reliability, and performance of the prime mover. In an attempt to address the changing conditions, multiple different sets of coefficients may be determined which each correspond to a different set of operating conditions. However, determining these multiple different sets of coefficients requires a significant amount of calibration workload. Further, the operating conditions of a prime mover may vary widely and it becomes increasingly difficult to obtain a set of coefficients for each different set of operating conditions. Any increase in the resolution of the operating conditions for which coefficients are determined, requires a corresponding increase in calibration workload to obtain those coefficients.

In accordance with an exemplary embodiment of the present disclosure, the thermal management system may significantly improve the ability to accurately control the temperature of the prime mover for a wide range of varying operating conditions by using a leveraged normalization factor. The inventors discovered that by comparing the energy balance across the thermal management system at a reference temperature to the energy balance of the thermal management system at actual temperatures across a wide range of operating conditions enables a scaling of the control system coefficients which accurately and reliably controls the prime mover temperature to a target temperature. In this manner, the control system coefficients may be continuously optimized across a wide variety of operating conditions while simultaneously obviating a large calibration workload.

The inventors discovered that the temperature of the heat exchanger 122 has a large impact upon the effectiveness of the heat exchanger 122 to reject heat and, therefore, its impact upon the temperature of the coolant entering the prime mover 102. For example, when the heat exchanger 122 is cold the impact of the heat exchanger 122 upon the coolant temperature is larger than when the heat exchanger 122 is warm. When the heat exchanger 122 is colder than the temperature at which the control system coefficients were determined, then any controller determined adjustment in the proportional volume between the two streams 116 and 118 may have a larger impact upon the temperature of the coolant at the inlet 120 than intended. This may lead to a potential overshoot in temperature and an instability in the temperature. In contrast, when the heat exchanger 122 is warmer than the temperature at which the control system coefficients were determined, then any controller determined adjustment in the proportional volume between the two streams 116 and 118 may have a smaller impact upon the temperature of the coolant at the inlet 120 than intended. This may lead to a significant increase in the delay with which the actual temperature of the coolant at the inlet 120 approaches the target temperature. In other words, this may result in an overdamped system.

To address and overcome these deficiencies, the inventors created a leveraged and normalized factor which scales the coefficients such that they are continuously optimized to provide improved control over the coolant temperature at the inlet 120. The inventors devised a coolant control valve leverage factor, F_(ccv), which is determined based upon:

$\begin{matrix} {F_{ccv} = \frac{\left( {{T\; 1} - {T\; 2}} \right)_{Standard}}{\left( {{T\; 1} - {T\; 2}} \right)_{Current}}} & (3) \end{matrix}$

Where (T1−T2)standard is the difference between the first temperature, T1, and the second temperature, T2, at a predetermined set of operating conditions and (T1−T2)current is the difference between the first temperature, T1, and the second temperature, T2, at current or actual conditions. Preferably, the operating conditions and corresponding temperatures, T1 and T2, are the same operating conditions and temperatures, T1 and T2, at which the control system coefficients were determined. For example, during a calibration procedure the prime mover 102 may be operated in an actual vehicle propulsion system and those coefficients which provide a desired and/or optimized control over the prime mover temperature for a given set of conditions may be determined and the temperatures, T1 and T2, for that set of conditions may then be set as the standard temperatures with which a value for (T1−T2)standard is stored and used for the calculation of F_(ccv).

Using F_(ccv), the coefficients for the control system may be continuously optimized. For example, in a control system using a proportional gain coefficient and an integral gain coefficient, the gains may be adjusted and/or compensated using:

K _(PC) =K _(P) ×F _(ccv); and   (4)

K_(IC) =K _(P) ×F _(ccv)   (5)

Where K_(P) is the proportional gain coefficient that was obtained during calibration, K_(I) is the integral gain coefficient that was obtained during calibration for a proportional/integral control system, K_(PC) is the compensated proportional gain coefficient, and K_(IC) is the compensated integral gain coefficient, where F_(ccv) is determined as described above.

Control over the coolant control valve 110 may then be based upon the following:

dV=K _(PC) ×T _(error) +K _(IC)×∫_(t−1) ^(t) T _(error) dt   (6)

Where dV is the change in volumetric flow rate between the bypass flow path 117 and the heat exchange flow path and T_(error) is determined in the same manner as explained above with reference to equations (2) and (3). dV may then be used to control the position of the coolant control valve.

FIGS. 2A and 2B are graphs which illustrate the improvement provided by an exemplary embodiment of the present disclosure over a conventional thermal management system. The vertical axes 200 for both graphs represent the magnitude of the coolant temperature at the inlet 120 while the horizontal axes 202 correspond to elapsed time. The horizontal dashed line 204 corresponds to a target temperature. FIG. 2A includes a line 206 which corresponds to the actual temperature at the inlet 120 for the conventional system and, similarly, FIG. 2B includes a line 208 which corresponds to the actual temperature at the inlet 120 for the thermal management system in accordance with an exemplary embodiment of the present disclosure. The responses which are illustrated for both FIGS. 2A and 2B correspond to operating conditions which differ from that which correspond to the operating conditions at which the control system coefficients were obtained. In this example, both systems have a heat exchanger temperature which is colder than that at which the corresponding control system coefficients were determined. The colder temperature of the heat exchanger corresponds to an increase in the effect the heat exchange flow path has upon the inlet temperature. For the conventional system, this results in proportional volume flow corrections being too large and an oscillation of the actual temperature above and below the target temperature. In other words, the conventional system is underdamped and potentially unstable.

These oscillations may further have an adverse impact upon the durability and reliability of the coolant control valve. Every time the temperature at the inlet fluctuates in FIG. 2A corresponds to a movement of the coolant control valve in response to the fluctuation. An inability of the system to settle the temperature means that the coolant control valve is repetitively operated.

In stark contrast, the response of the thermal management system in accordance with an exemplary embodiment of the present disclosure which uses the leveraged and normalized factor, F_(CCV), as described above to adjust or compensate the control system coefficients provides an improved temperature response 208 which better follows the target temperature 204. This further reduces and/or eliminates the requirement for the coolant control valve to continuously adjust. The coolant control valve may be accurately and appropriately positioned immediately and/or much sooner which significantly reduces the wear and improves the reliability and durability of the coolant control valve.

FIG. 3 is a flowchart 300 of a method in accordance with an exemplary embodiment of the present disclosure. The method starts at step 302 and continues to step 304. In step 304, the method senses a first temperature with a first temperature sensor 124 in a bypass flow path 116, a second temperature with a second temperature sensor 126 in a heat exchange flow path 118, and third temperature with a third temperature sensor 128 at the engine coolant inlet 120 and continues to step 306. In step 306, the method normalizes a gain coefficient in a closed loop controller based upon the first and second temperatures. The method then continues to step 308, where a controller 112 determines a difference between the third temperature and a target temperature at the engine coolant inlet 120 (an error). The method then continues to step 310 where the controller 112 generates a command signal for a coolant control valve 110 based upon the error and the normalized gain coefficient and continues to step 312. In step 312, the method operates a coolant control valve 112 based upon the command signal from the controller 112.

This description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. 

1. A vehicle propulsion system, the system comprising: a prime mover having a coolant inlet and a coolant outlet; a coolant control valve having a valve inlet in communication with the prime mover coolant outlet, a first valve outlet, and a second valve outlet; a bypass flow path in communication with first valve outlet and the prime mover coolant inlet; a heat exchange flow path in communication with the second valve outlet and the prime mover inlet; a heat exchanger in the heat exchange flow path; a first temperature sensor in the bypass flow path for generating a first temperature signal; a second temperature sensor in the heat exchange flow path for generating a second temperature signal; a third temperature sensor at the prime mover coolant inlet for generating a third temperature signal; and a controller in communication with the first temperature sensor for receiving the first temperature signal, the second temperature sensor for receiving the second temperature signal, the third temperature sensor for receiving the third temperature signal, and the coolant control valve for providing a coolant control valve command signal to the coolant control valve, wherein the controller comprises a closed loop controller with a gain coefficient, and wherein the controller normalizes the gain coefficient, and wherein the controller is further in communication with the coolant control valve and controls the coolant control valve based upon the normalized gain coefficient.
 2. The system of claim 1, wherein the closed loop controller comprises a proportional/integral closed loop controller.
 3. The system of claim 2, wherein the gain coefficient comprises one of a proportional gain coefficient and an integral gain coefficient for the proportional/integral closed loop controller.
 4. The system of claim 1, wherein the controller normalizes the gain coefficient based upon a ratio of a predetermined difference in values between a first temperature signal and the second temperature signal and a current difference in values between a first temperature signal and the second temperature signal.
 5. The system of claim 4, wherein the predetermined difference in values between a first temperature signal and the second temperature signal correspond to a first temperature signal value and a second temperature signal value which both correspond to the gain coefficient.
 6. The system of claim 1, wherein the second temperature sensor is downstream of the heat exchanger in the heat exchange flow path.
 7. The system of claim 1, wherein the bypass flow path and the heat exchange flow path combine to form a prime mover coolant inlet flow path at the prime mover coolant inlet.
 8. The system of claim 7, wherein the third temperature sensor is positioned in the prime mover coolant inlet flow path.
 9. A method for controlling prime mover temperature in a vehicle propulsion system having a coolant control valve with a valve inlet in communication with a coolant outlet of the prime mover, and a first valve outlet in communication with a bypass flow path, and second valve outlet in communication with a heat exchange flow path, the heat exchange flow path including a heat exchanger, wherein the bypass flow path is in communication with first valve outlet and a prime mover coolant inlet, the method comprising: sensing a first temperature with a first temperature sensor in the bypass flow path; sensing a second temperature with a second temperature sensor in the heat exchange flow path; normalizing a gain coefficient in a closed loop controller based upon the first and second temperatures; generating a command signal for the coolant control valve based upon the normalized gain coefficient; and operating the coolant control valve based upon the command signal.
 10. The method of claim 9, wherein the closed loop controller comprises a proportional/integral closed loop controller.
 11. The method of claim 10, wherein the gain coefficient comprises one of a proportional gain coefficient and an integral gain coefficient for the proportional/integral closed loop controller.
 12. The method of claim 9, wherein normalizing the gain coefficient is based upon a ratio of a predetermined difference in first temperature and second temperature and a current difference in values between first temperature and second temperature.
 13. The method of claim 12, wherein the predetermined difference in first temperature and second temperature both correspond to the gain coefficient.
 14. The method of claim 9, wherein the second temperature sensor is downstream of the heat exchanger in the heat exchange flow path.
 15. The method of claim 9, wherein the bypass flow path and the heat exchange flow path combine to form a prime mover coolant inlet flow path at the prime mover coolant inlet.
 16. The method of claim 15, wherein the third temperature sensor is positioned in the prime mover coolant inlet flow path. 